There currently exists a problem in transporting gaseous substances such as natural gas and hydrogen by road, rail and sea under refrigerated conditions due to the weight, potential danger of failure, and/or the cost of the pressure vessel systems available. As is known, steel systems are very heavy and are prone to corrosion. They are also limited to near ambient storage temperatures as the potential danger of a brittle/ductile failure exists due to Joule Thompson effects caused by decompression. This is a significant restriction on potential applications as the refrigeration of compressed gases generally increases density thus, increases the net capacity within the same volume of storage space, therein increasing cost efficiency and potential profitability.
Type 2 pressure vessel systems have similar weight and corrosion problems.
Type 3 pressure vessel systems using carbon steel liners also have similar weight and corrosion problems as well as potential ductility problems at lower temperatures.
Type 3 pressure vessel systems made with aluminum liners overcome the weight and the ductility problems to a certain extent at reduced temperatures, however, aluminum is prone to corrosion. Thus, there still exists the danger of a potential failure due to corrosion, especially at the piping interface. In addition, type 3 pressure vessels with aluminum liners can only be cost-efficiently made seamless up to a limited diameter. Thus, for the bulk storage and/or transport of gaseous fluids using such type 3 pressure vessels, a lot of pressure vessels would be required. This would require a large number of connections, each one being a potential source of failure. This decreases the level of safety of this alternative. Further still, the large number of such relatively small type 3 pressure vessels and respective connections required to justify a bulk transportation project may make such a project infeasible. The same potential problem of a large number of connections would exist with relatively small diameter type 4 pressure vessels.
Currently, type 4 cylinders made from extruded high density polyethylene (HDPE) pipe and injection-molded domes with polar port bosses are being marketed in a long horizontal arrangement. However, due to the design of these tanks, they cannot be refrigerated. As noted above, this incurs a disadvantage to capacity and therefore, potential economic feasibility. The problems with the design of the current type 4 pressure vessels made from extruded HDPE pipe and injection molded domes under refrigerated conditions are numerous. Firstly, the toe-in effect of extruded HDPE pipe leaves a circumferential indentation at the pipe end and injection-molded dome edge weld line. This creates a discontinuity in circular diameter at the weld line. Should the pressure vessel be refrigerated, the volumetric shrinking of the liner relative to the laminate shell will create a stress concentration at the weld line. This is an undesirable condition as it could be the source of a liner failure.
The second potential problem with refrigerating this design of pressure vessel is in the design of the port boss liner interface. As the port boss is inset into an injection mold, it uses the cooling and the related contracting effect to seal the HDPE material onto the opposing tabs and slots of the port boss. Thus, once the pressure vessel is completely fabricated, any additional refrigeration would create further contracting of the HDPE material which may pull the material away from the tabs and slots or tear the liner material at this location. Neither of these would be a desirable consequence as the integrity of the liner would then be compromised.
Further still, even if the known type 4 cylinders could be refrigerated, two other problems would exist. The first is the potential of overturning in a road or rail application due to sloshing. When refrigerated under pressure, many gaseous substances such as natural gas become partially liquid or fluid like. A fluid like substance would create an end impact when braking is applied. This impact force could overturn or cause damage to the rather long pressure vessel(s) and/or related support system. The second problem that would be inherent with a horizontal arrangement of refrigerated pressure vessels with polar port bosses is that condensed liquids cannot be removed without vaporizing the liquids. This may be infeasible and/or impractical in refrigerated systems. Thus, even if the currently marketed type 4 pressure vessels could be refrigerated, other problems are perceived to exist due to condensed liquids.
There is an additional problem inherent in the current design of extruded HDPE pipe with injection-molded domes that is unrelated to refrigeration. It deals with the wall thickness of injection-molded parts. Such parts are inherently thin (relatively speaking). This potentially creates a significant deficiency in stability of the liner during the winding process. As the relatively thin-walled plastic domes have to carry the full weight of the liner/mandrel, filament fibers and wet resin, the amount of filament fiber and resin and thus maximum operating pressure of the pressure vessels in this manner is limited. Similarly, so is the type of filament fiber applicable. Notably, fiberglass is heavier than carbon fiber for comparable operating pressures. In summary, this design limits use to only carbon fiber and at limited operating pressures.
Accordingly, there is a need for a novel intermodal container or road trailer system for storing and/or transporting gaseous fluids.